## Thinking Mathematically (6th Edition)

a. 2.65 (million) b. $p=203.3+2.65*x$ c. $335.8$ million
a. To estimate the yearly average increase, we need to: 1. subtract the value at 1970 from the value at 2010. $309.3-203.3=106$ 2. Divide it by the number of years between them. $106\div(2010-1970)=106\div 40=2.65$ The estimated average yearly increase is $2.65$ (million). b. To write the mathematical model ($p$), we need to take the population in 1970 (203.3) and add to it the estimated yearly average ($2.65$) for every year that passed (x). $p=203.3+2.65*x$ c. Using the model in (b), we can estimate that the population in 2020 will be: $p=203.3+2.65*(2020-1970)=203.3+132.5=335.8$ (million)